Comparison of the effects of a conventional heat treatment between cast and selective laser melted IN939 alloy

Additive manufacturing (AM) is a process where, as the name suggests, material is added during production, in contrast to techniques such as machining, where material is removed. With metals, AM processes involve localised melting of a powder or wire in specific locations to produce a part, layer by layer. AM techniques have recently been applied to the repair of gas turbine blades. These components are often produced from nickel-based superalloys, a group of materials which possess excellent mechanical properties at high temperatures. However, although the microstructural and mechanical property evolution during the high temperature exposure of conventionally produced superalloy materials is reasonably well understood, the effects of prolonged high temperature exposure on AM material are less well known. This research is concerned with the microstructures of components produced using AM techniques and an examination of the effect of subsequent high temperature exposures. In particular, the paper will focus on the differences between cast and SLM IN939 as a function of heat treatment and subsequent ageing, including differences in grain structure and precipitate size, distribution and morphology, quantified using advanced electron microscopy techniques.